Farfield criteria for vibrating structures: Numerical simulation on plates and cylinders

Abstract

In order to determine practical criteria for the nearfield/farfield transition in the case of underwater vibrating structures, the acoustic field radiated by plates and cylinders is simulated. Various mode shapes of these structures are computed for different frequencies including their resonance frequencies. These calculations are made for radiators of different sizes and are compared with the results of a mechanical simulation for a point‐excited ribbed cylinder. Then the distances at which the pressure field is at ± 1 dB of the farfield value, the wave specific impedance is ρc ± 12% (1 dB), and pressure and velocity have a phase difference of less than ± 15° are tabulated as a function of frequency. The envelope of these points is compared with the standard criterion (R ≫ λ and R ≫ L2/λ). Finally, various criteria are proposed depending on which property of the farfield is required.